There are two basic faceplate panel contours utilized commercially for rectangular CRT's of screen sizes greater than about a 23 cm diagonal: spherical, and cylindrical. Although flat contours are possible, the added thickness and weight of the faceplate panel required to maintain the same envelope strength are undesirable. Furthermore, if a flat faceplate CRT is a shadow mask color picture tube, the additional weight and complexity of an appropriate shadow mask also are undesirable.
A new faceplate panel contour concept is disclosed in three recently-filed copending U.S. Applications: Ser. No. 469,772, filed by F. R. Ragland, Jr. on Feb. 25, 1983; Ser. No. 469,774, filed by F. R. Ragland, Jr. on Feb. 25, 1983; and Ser. No. 469,775, filed by R. J. D'Amato et al. on Feb. 25, 1983 abandoned. The contour has curvature along both the major and minor axes of the faceplate panel, but is nonspherical. In a preferred embodiment described in these applications, the peripheral border of the tube screen is planar. In such tubes, it is important to contour the faceplate panel diagonals so that the differing curvatures extending from the major and minor axes are properly blended. In the above-cited U.S. Application Ser. No. 469,774, this blending is accomplished by permitting at least one sign change of the second derivative of the diagonal contour in the center-to-corner direction.
The present invention provides a novel faceplate panel contour which does not have an inflection along the diagonal contour.